1. Field of the Invention
The present invention relates generally to gas diffusion testing of materials, and, more particularly, to closed system testing of materials for their permeability to specific gases.
1. Description of the Related Art
The prior art has long recognized the need for a system capable of testing building or other materials for their ability to prevent or allow diffusion of undesirable or desirable gases, respectively.
One prior art system for testing the capability of structural materials to prevent diffusion of radon gas is the "bucket test", which entails the use of two five-gallon buckets placed end to end. The opposed ends of the buckets are structured to remain open to each other save for the material to be tested, which is placed between the two openings so that gas passing from one bucket to the other necessarily diffuses across the test material. A radon source placed in the first, or "hot", bucket, provides the radon gas whose presence sensed in the second, or "cold", bucket, when compared to the hot bucket gas concentration, indicates the capacity of the test material to prevent diffusion of the radon gas. Such testing has been carried out at atmospheric pressure, with no direct control over the concentration of radon in the hot bucket.
A gas commonly found in inhabited areas, yet undesirable there, is radon gas. Radon is a radioactive elemental product of certain materials often found in the earth's crust. Due to its nature as a pressure-driven gas, it finds its way into buildings under the influence of pressure differentials present across the building structure. In particular, a "sealed" building, such as one closed for heating in winter or for cooling in summer, is susceptible to radon diffusion when external pressure changes cause differentials that cannot equilibrate quickly. A system for accurately testing a material sample for its diffusion characteristics under the influence of a pressure-driven gas, under conditions similar to actual use conditions, would give more useful information with respect to predicting in situ performance of the material.